n- and p-type CsPbBr3 Nanocrystals via Electrochemical Doping

Electronic doping underpins many semiconductor applications, but it has remained elusive for lead halide perovskite nanocrystals because their high density and low formation energy of defects easily compensate introduced dopants. Here we use electrochemical doping as a strategy to avoid doping compensation. Electrochemical injection of electrons or holes into the nanocrystal is compensated by surface-adsorbed electrolyte counterions, therefore not compromising crystal structure. We accomplished ambipolar (n- and p-type) doped CsPbBr3 nanocrystals with charge carrier concentrations up to the heavy doping regime (4.8x10 17 cm −3 , corresponding to 0.25 charges per nanocrystal). We show that electrochemical doping is reversible and stable at these high free carrier concentrations. The high extent of doping and stability is enabled by the use of lecithin, a zwitterionic ligand that strongly binds to the surface of the CsPbBr 3 nanocrystals while still allowing ion and electron transfer. Lecithin stabilizes the surface atoms by shifting the potentials for Pb2+ reduction and Br- oxidation outside of the bandgap. The inferred surface-chemistry design rules for stable electrochemical doping can also serve as a guideline for developing CsPbBr 3 nanocrystals stable under high free-carrier concentrations in optoelectronic devices, such as light-emitting diodes or electronically triggered quantum light sources.